The Telescoping series reference article from the English Wikipedia on 24-Apr-2004
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Telescoping series

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In mathematics, telescoping series is an informal expression referring to a series whose sum can be found by exploiting the circumstance that nearly every term cancels with a succeeding or preceding term.

For example, the series

simplifies as

While telescoping is a neat technique, there are pitfalls to watch out for:

is not correct because regrouping of terms is invalid unless the individual terms converge to 0.